1. Technical Field
The present invention relates to a toner for use in electrostatic image development and a preparation method thereof.
2. Related Art
Electrostatic image development as represented by electrophotography is broadly employed in imaging methods using printers, copiers or facsimile devices.
This is due to a very matured method whereby high quality images can be obtained at a high speed but some problems still remain. In a conventional toner prepared by a pulverization method, for example, a material dispersed in the toner exists nonuniformly on the fracture face, making it difficult to form a uniform surface property among toner particles and easily causes scattering in the transfer process, producing problems such as deteriorated color reproduction of a color image.
Further, particle size reduction has been desired for toners for use in electrostatic image development to achieve higher image quality. Recently, development of polymerization toners has been actively conducted to prepare a size-reduced toner. Preparation of polymerization toners include a method in which resin particles and colorant particles are allowed to be associated through salting-out, flocculation and coalescence to form irregular-form toner, and a method in which a radical-polymerizable monomer and a colorant are mixed and dispersed in an aqueous medium in the form of droplets of a desired size to undergo suspension polymerization.
Application of suspension polymerization forms spherical toner particles exhibiting a uniform surface quality, leading to enhanced homogeneity among toner particles, but the spherical form enhances adhesion onto a latent image carrier, producing problems such as lowered transferability.
JP-A No. 11-194540 (hereinafter, the term, JP-A refers to unexamined Japanese Patent Application Publication) discloses non-spherical particles prepared by treating particulate resin polymerized in an aqueous medium containing a surfactant using a flocculant at a concentration more than the critical flocculation concentration and an organic solvent exhibiting unlimited solubility in water.
The foregoing technique uses di-valent or tri-valent metal salts as a flocculent, resulting in superior uniformity in form and electrostatic charge, leading in turn to images exhibiting superior sharpness, while the presence of the di-valent or tri-valent metal salts raises a Krafft point of a surfactant, forming hardly water-soluble deposits. Even after separating colored particles or a toner from an aqueous medium, such deposits are present in an adhered form to the toner, producing problems such that fine-line reproduction is easily degraded and crushed print (or blocking of characters) easily occurs.
Commonly known nonionic surfactants have been used as an emulsifier of emulsion polymerization and specifically, a nonylphenol type nonionic surfactant has been generally used. The nonyl phenol type nonionic surfactant can be easily applicable in terms of enhanced emulsifying capability. On the other hand, it is difficult to cause its biodegradation due to structure, and it is also difficult to control the particle size in the preparation of toner particles using emulsion polymerization particles, resulting in widened toner particle size distribution and producing problems such as inferior fine-line reproduction and crushed print. Further, polyoxyalkylene alkyl ethers, which are also applicable to emulsion polymerization, exhibit inferior emulsifying capability to the nonylphenol type, so that the amount to be used becomes larger, resulting in remaining in the toner and producing problems such as widened tone article size distribution, inferior fine-line reproduction and crushed print. Accordingly, an emulsifying agent suitable for emulsion polymerization is still being explored.